The relationship between diet and cognitive function has been a topic of increasing interest, as numerous studies have shown that variations in dietary practices and nutrient intake may protect against age-related cognitive decline, as well as the development of dementia and Alzheimers Disease (AD). Various dietary practices and specific nutrient components of these diets have been examined in relation to cognitive performance including 1) dietary fatty acids (including fish oil) and the Mediterranean diet, 2) antioxidants (including vitamins E and C) and fruits and vegetables, 3) vitamins B6, B12 (cobolamine), and folate, and, more recently, 4) caloric restriction. Although observational studies have generally reported significant associations between dietary practices and reduced incidence of cognitive dysfunction, randomized trials of dietary interventions have yielded mixed findings, with many trials yielding small gains or equivocal findings. In addition, findings appear to vary based on sample characteristics, methods of dietary assessment, and length of study follow-up. The influence of dietary practices on cognitive function in middle aged and older adults remains uncertain, and further research is needed to clarify the nature of this relationship and identify mechanisms by which diet may affect neurocognition.